docs(readme): replace fastify.io links with fastify.dev (#426)

* docs(readme): replace `fastify.io` links with `fastify.dev`

* docs(readme): remove `www.` from `fastify.dev` urls

Author: Fdawgs

README.md

@@ -124,7 +124,7 @@ A URL path prefix used to create a virtual mount path for the static directory.
 Default: `{}`
 
 Constraints that will be added to registered routes. See Fastify's documentation for
-[route constraints](https://www.fastify.dev/docs/latest/Reference/Routes/#constraints).
+[route constraints](https://fastify.dev/docs/latest/Reference/Routes/#constraints).
 
 #### `prefixAvoidTrailingSlash`
 
@@ -450,7 +450,7 @@ decorators.
 
 If a request matches the URL `prefix` but a file cannot be found for the
 request, Fastify's 404 handler will be called. You can set a custom 404
-handler with [`fastify.setNotFoundHandler()`](https://www.fastify.dev/docs/latest/Reference/Server/#setnotfoundhandler).
+handler with [`fastify.setNotFoundHandler()`](https://fastify.dev/docs/latest/Reference/Server/#setnotfoundhandler).
 
 When registering `@fastify/static` within an encapsulated context, the `wildcard` option may need to be set to `false` in order to support index resolution and nested not-found-handler:
 
@@ -475,7 +475,7 @@ This code will send the `index.html` for the paths `docs`, `docs/`, and `docs/in
 
 If an error occurs while trying to send a file, the error will be passed
 to Fastify's error handler. You can set a custom error handler with
-[`fastify.setErrorHandler()`](https://www.fastify.io/docs/latest/Reference/Server/#seterrorhandler).
+[`fastify.setErrorHandler()`](https://fastify.dev/docs/latest/Reference/Server/#seterrorhandler).
 
 ### Payload `stream.filename`